It is.
Unfortunately, the folks who wrote that clause incorrectly assumed that Congress would only pass laws addressing matters that were explicitly delegated to the federal government in the Constitution, because everything else was, "reserved to the States respectively, or to the people."
If one reads the whole thing quite literally, one can easily come to the conclusion that about 90% of everything the FedGov does is illegitimate because it is not explicitly authorized to do those things by the Constitution.
Can't argue with this entirely Either.
For the Issue being Discussed, I think the Federal Law should be Upheld/Enforced. Because Choosing to Enforce a Law shifts the Role of the Justice Department to something I'm Not all that comfortable with. As WH or Justice Dept leadership changes, the Law shouldn't.
That said, I think we live in a Different Time than when things were put on a certain "Schedule".
And if there is Really as much support to Change a Law that has become Outdate, then so be it. Congress should consider changing the Law. And not want/ask the AG to just look the Other way.